Self-adhesive air cushion film as protection for fresh paint finishes during vehicle assembly, and production process

ABSTRACT

A self-adhesive air cushion film for temporary protection of fresh paint surfaces of vehicles such as automobiles and freshly painted vehicle parts, having a first carrier film on which a second, bubble-forming carrier film is present, the bubbles being filled in particular with air, a sheet of polyethylene being inseparably applied at least partially to the bubbles, and a self-adhesive layer being applied to the film.

The invention relates to a self-adhesive air cushion film as protectionfor fresh paint finishes during vehicle assembly, to processes for theproduction, and to possible uses thereof.

Self-adhesive air cushion films as packaging materials for sensitiveproducts are a conventionality. One particularly preferred grade, whichis distinguished by the longevity of the air cushions and also by arear-face masking sheet for the air cushions, so that the carrier sheetdoes not remain without cushioning between the cushions, is known underthe brand name AirCap® from the company Sealed Air.

This air cushion film is distinguished by the fact that a three-layerconstruction of the film from polyethylene/barrier layer/polyethyleneprevents air emerging from the individual bubbles in the film.

Applying self-adhesive air cushion films to freshly painted bodies invehicle manufacture, especially automobile manufacture, harbors the riskthat, beneath the adhesive of the self-adhesive air cushion film, thepaint finishes, which immediately after their drying have not yetattained their final state and which consequently are soft and possiblyalso are still giving off condensates in gaseous form from crosslinking,will undergo irreversible deformation and/or discoloration.

Self-adhesive sheets which are intended for adhering to freshly paintedbodies and which in extreme cases are required to remain on the paintfinish throughout the assembly of the vehicle and throughout the chainof transit ending with the dealer, who prepares the vehicle, possiblyafter some time in storage, for display and/or for transfer to thepurchaser, and which are expected not to give rise to irreversibledeformation or discoloration of the paint finish, are also aconventionality. One preferred embodiment is produced by tesa AG andsold under the brand name tesa® Bodyguard.

By way of example, a paint protection sheet may be noted which is basedon polyethylene-vinyl acetate (EVA) and is described in DE 195 32 220A1. This system attains good bonding values after just a short time andensures a high degree of bonding security against unwanted andunprompted detachment in transit. Disadvantages perceived by the userinclude the strong peel increase, which can be lessened with a mixtureof different EVA copolymers as described in DE 100 50 499 A1.

For practical purposes in vehicle assembly, however, self-adhesiveprotective sheets of this kind frequently afford too little protectionagainst mechanical exposure and are frequently adhered belowself-adhesive air cushion films, rigid shells or cushioned covers inorder to prevent these systems acting on the fresh paint finish. Thisapproach implies additional worksteps and hence costs in vehiclemanufacture both during application and during removal of the assemblyprotection measures.

It is an object of the invention to combine an air cushion film and apaint protection sheet into one product and to do so in a cost-effectiveway by using a modification of the paint protection sheet as an integralconstituent in the production of the air cushion film, as a rear-facemasking sheet.

This object is achieved by means of a self-adhesive air cushion film asdescribed in the main claim. The dependent claims provide particularlyadvantageous embodiments of the subject matter of the invention, andalso particularly advantageous uses of and production processes for theair cushion film of the invention.

The invention accordingly provides a self-adhesive air cushion film fortemporary protection of fresh paint surfaces of vehicles such asautomobiles and freshly painted vehicle parts, having a first carrierfilm on which a second, bubble-forming carrier film is present, thebubbles being filled in particular with air, a sheet of polyethylenebeing inseparably applied at least partially to the bubbles, and aself-adhesive layer being applied to the film.

In one first advantageous embodiment of the invention there is anadhesion promoter layer between the sheet and the layer of adhesive.

Furthermore, preferably, the first carrier film, the second carrier filmand/or the sheet may contain at least one light stabilizer in an amountof at least 0.15% by weight and/or titanium dioxide, preferably in anamount of 5% to 15% by weight.

In one advantageous embodiment the second carrier film features athree-layer construction comprising polyethylene sheet/barrierlayer/polyethylene sheet.

The first carrier film may be composed of polyolefins such aspolyethylene, polypropylene, their blends or copolymers. The firstcarrier film may also be designed as a foam layer. It is within theconcept of the invention, furthermore, to configure the first carrierfilm as a polyethylene-coated paper carrier.

For the self-adhesive compound a variety of adhesives may be usedwithout restricting the utility of the sheet.

It is applied to the sheet preferably at coatweights of between 3 and 35g/m², preferably between 8 and 20 g/m². Application may take place fromsolution, in hexane or benzene, for example, or else from the melt.

In one further preferred embodiment the self-adhesive compound iscomposed of butyl rubber, the isoprene fraction in the butyl rubberbeing preferably up to 1.2 mol percent, more preferably up to 1.8 molpercent.

Butyl rubbers are copolymers of isobutene and isoprene which areprepared by cationic polymerization in solution. The isoprene fractionvaries typically between 0.5 and 5 mol percent. The isoprene is normallyincorporated in 1,4 addition, so that, in contrast to polyisobutylenehomopolymer, this polymer has double bonds in the main chain.Accordingly it constitutes a link between a straight poly-cis-isoprene,or natural rubber, and a polyisobutylene homopolymer.

A further group of butyl rubbers is that of the starbranched types,where more intensive branching is achieved through comonomers such asdivinylbenzene. More recently, butyl rubbers having lateral double bondshave also been disclosed (1,2 and/or 3,4 addition of the isoprene), andare suitable in accordance with the invention.

Manufacturers of such products are in particular the companies Bayer(Bayer Butyl) and Exxon (Exxon Butyl).

In order to obtain sufficient cohesion for an adhesive application,particularly at elevated temperatures, the molar mass advantageously atleast of part of the polyisobutylenes used is relatively high, generallyat least 200 000 g/mol (number-average Mn).

The butyl rubbers, similarly to polyisobutylenes of medium molecularweight, are indeed inherently tacky. Nevertheless, in order to optimizetheir properties, particularly the adhesion characteristics, theadhesive compound of the protective sheet of the invention canadvantageously be blended with one or more additives. Possible suchadditives include tackifiers (tackifier resins which optimizepressure-sensitive adhesion qualities), plasticizers, organic orinorganic fillers, pigments, light stabilizers, including those in theform of UV-absorbing, sterically hindered amines (HALS), aginginhibitors in the form, for example, of lactones, primary and secondaryantioxidants, or further elastomers. As an option, crosslinking agentsand crosslinking promoters may be added to the self-adhesive compound.An exhaustive selection of crosslinking agents and crosslinkingpromoters are described in Ullmann's Encyclopedia of IndustrialChemistry (6th Edition, 2003), sections “Rubber, 4. Chemicals andadditives” and “Manual for Rubber Industry”, Bayer AG (1995).

Examples of possible elastomers for modifying the self-adhesive compoundinclude polyisobutylenes, polyolefin copolymers such as EPM or EPDM,polybutenes, hydrogenated block copolymers of styrene and dienes, oracrylate copolymers. These elastomers are used in proportions in therange from 0 to 20 parts by weight, preferably below 10 parts by weightper 100 parts by weight of butyl rubber.

Examples of suitable tackifiers include synthetic hydrocarbon resins (ofC₅ or C₉ monomers, for example), natural resins, polyterpene resinsbased on α-, β-pinene or γ-limonene, rosin and rosin derivatives, andothers, as listed in Ullmann's Encyclopedia of Industrial Chemistry (6thEdition, 2003), sections “Resins-Synthetic” and “Resins-Natural”. Use ismade primarily of fully or partly hydrogenated resins, which are morestable toward aging. In the adhesive of the protective sheet of theinvention it is preferred to use 0 to 50 parts by weight, in particular0 to 20 parts by weight, of a tackifier, based on 100 parts by weight ofbase polymer.

Examples of suitable plasticizers for the self-adhesive compound includealiphatic, cycloaliphatic, and aromatic mineral oils, diesters orpolyesters of phthalic, trimellitic or adipic acid, liquid rubbers(nitrile or polyisoprene rubbers, for example), liquid polymers (ofisobutene or ethylene/propylene), acrylic esters, polyvinyl ethers,liquid resins and soft resins based on the raw materials of tackifierresins, lanolin and other waxes, or liquid silicones. Aging-stableplasticizers without an olefinic double bond are particularly suitable.It is preferred to use 0 to 40 parts by weight, in particular 0 to 10parts by weight, of a plasticizer, based on 100 parts by weight of basepolymer.

In a further advantageous embodiment the layer of adhesive is composedof a mixture of synthetic rubbers:

-   -   a) the layer of adhesive being composed of a polar component A        and an apolar component B,    -   b) the polar component A being present in a fraction of 50% to        99% by weight and consisting of a copolymer or mixture of        copolymers of ethylene and vinyl acetate whose vinyl acetate        content is between 40% and 80% by weight, and    -   c) the apolar component B being present in a fraction of 1% to        50% by weight and consisting of one or a mixture of homopolymers        or copolymers of α-olefins having 2 to 12 carbon atoms, these        polymers being saturated in the main chain and being amorphous        or having a low degree of crystallinity.

Alternatively the apolar component B may be present in a fraction of 1%to 50% by weight and may consist of copolymers of α-olefins having 2 to12 carbon atoms and nonconjugated dienes.

Suitable products for the polar component of the adhesive includeethylene-vinyl acetate (EVAc) grades whose VAc fraction is between 40%and 80% by weight, preferably between 50% and 70% by weight. It is alsopossible to blend different EVAc grades. Compounds suitable for theapolar component include poly-α-olefins such as polyisobutylene (PIB),poly-1-butene (PB), ethylene-propylene copolymers (EPM),ethylene-propylene-diene terpolymers (EPDM), the diene beingnonconjugated, poly-1-hexene, poly-1-octene, and other copolymers ofethylene and α-olefins having 4-12 carbon atoms that are amorphous orhave a low degree of crystallinity. The apolar polymers as well can beblended in order to obtain optimum properties.

In one further advantageous embodiment the self-adhesive compound iscomposed of polyethylene-vinyl acetate at a vinyl acetate content of 40%to 80% by weight, in particular 70% by weight, and with a loss angle tanδ of 0.6 to 1.0, measured at a temperature of 60° C. and a frequency of10⁻² Hz, and of 0.4 to 0.7, measured at a temperature of 60° C. and afrequency of 10 Hz, the target properties.

The self-adhesive compound may be applied to the sheet from solution orfrom the melt. The self-adhesive layers as elucidated in more detailabove may with advantage be blended with one or more additives such astackifiers, plasticizers, organic or inorganic fillers, pigments, lightstabilizers, preferably in the form of UV-absorbing, sterically hinderedamines (HALS), aging inhibitors, preferably in the form of lactones,primary and secondary antioxidants, crosslinking agents and/orcrosslinking promoters.

With particular advantage the self-adhesive air cushion film of theinvention may be produced by the following process:

Arriving from an extruder, the second carrier film is cast through a dieonto a transfer roll. The transfer roll lays the second carrier filmonto a thermoforming roll, containing bubble-shaped depressions and avacuum zone.

As it traverses the vacuum zone of the thermoforming roll, the secondcarrier film is drawn into the depressions in the thermoforming roll andthus forms the air-filled bubbles. Immediately following departure fromthe vacuum section of the thermoforming roll, and likewise arriving froman extruder, the first carrier film is applied through a die onto afurther transfer roll and is transferred from the transfer roll to thethermoformed second carrier film.

Finally, the sheet of polyethylene, provided with a self-adhesive layer,is applied in a laminating station, consisting of two rolls, to thebubbles in the second carrier film, a procedure which takes place withapplication of pressure, which flattens the air-filled bubbles at thetip but does not compress them, and with application of heat, with hotair at approximately 180° C. being passed through a hot-air nozzle intothe nip formed by the sheet and the second carrier film as they arebrought together, so that the sheet is inseparably welded to the tips ofthe bubbles.

In accordance with further versions of the production process, theprocessing properties of the self-adhesive air cushion film thusproduced can be enhanced by passing it through a perforation station inwhich perforations are made in the air cushion film at a distance, forexample, of 250 mm, so that the film can be drawn off by hand. As afurther option, the self-adhesive air cushion film can be trimmed at theproduction edges, divided into narrower strips, and wound up to formrolls.

In this form in particular, the air cushion film of the invention can beemployed directly in the vehicle manufacturer's assembly process withoutfurther tools or apparatus.

With particular advantage the air cushion film of the invention can beused as assembly and/or transit protection on freshly painted surfacesof automobiles or automobile parts and also in general for protectingsensitive paint, metal, wood, plastic or glass surfaces.

By means of the figures described below, the air cushion film of theinvention is elucidated in more detail in a particularly advantageousversion, as is also a process for production thereof, without anyintention that the invention should be unnecessarily restricted as aresult. In the drawing

FIG. 1 shows the air cushion film of the invention and

FIG. 2 shows a process for producing the air cushion film of theinvention according to FIG. 1.

According to FIG. 1 the self-adhesive air cushion film 5 consists of afirst carrier film 1, in this case a polyethylene sheet, on which thereis a second carrier films, forming bubbles 2 a, the bubbles 2 a beingair-filled.

Joined to the tips of the bubbles 2 a is a multilayer sheet 3, a sheetof polyethylene 3 a being applied inseparably to the tips of the bubbles2 a. The polyethylene sheet 3 a is provided with a self-adhesive coating3 c, there being an adhesion promoter layer 3 b present between sheet 3a and adhesive 3 c.

FIG. 2 shows the production process of the air cushion film of theinvention according to FIG. 1.

Arriving from an extruder, the second carrier film 2 is cast through adie 10 onto a transfer roll 11.

The transfer roll 11 lays the second carrier film 2 onto a thermoformingroll 12, containing bubble-shaped depressions 13 and a vacuum zone 14,which extends over a quarter of the thermoforming roll 12 (90°).

As it traverses the vacuum zone 14 of the thermoforming roll 12, thesecond carrier film 2 is drawn into the depressions 13 in thethermoforming roll 12 and thus forms the air-filled bubbles 2 a.

Immediately following departure from the vacuum section 14 of thethermoforming roll 12, and likewise arriving from an extruder, the firstcarrier film 1 is applied through a die 15 onto a further transfer roll16 and is transferred from the transfer roll to the thermoformed secondcarrier film 2.

Finally, the sheet 3 of polyethylene, provided with a self-adhesivelayer, is applied in a laminating station, consisting of two rolls 21and 22, to the bubbles 2 a in the second carrier film 2, a procedurewhich takes place with application of pressure, which flattens theair-filled bubbles 2 a at the tip but does not compress them, and withapplication of heat, with hot air at approximately 180° C. being passedthrough a hot-air nozzle 23 into the nip formed by the sheet 3 and thesecond carrier film 2 as they are brought together, so that the sheet 3is inseparably welded to the tips of the bubbles 2a.

1. Self-adhesive air cushion film for temporary protection of freshpaint surfaces of vehicles and freshly painted vehicle parts, having afirst carrier film on which a second, bubble-forming carrier film ispresent, the bubbles being filled with air, a sheet of polyethylenebeing inseparably applied at least partially to the bubbles, and aself-adhesive layer being applied to the film.
 2. Self-adhesive aircushion film according to claim 1, having an adhesion promoter layerbetween the sheet and the layer of adhesive.
 3. Self-adhesive aircushion film according to claim 1, wherein the first carrier film, thesecond carrier film and/or the sheet contain at least one lightstabilizer in an amount of at least 0.15% by weight and/or titaniumdioxide, in an amount of 5 to 15% by weight.
 4. Self-adhesive aircushion film according to claim 1, wherein the second carrier film has athree-layer construction comprising polyethylene sheet/barrierlayer/polyethylene sheet.
 5. Self-adhesive air cushion film according toclaim 1, wherein the first carrier film is composed of polyolefinsselected from the group consisting of polyethylene, polypropylene andtheir blends or copolymers.
 6. Self-adhesive air cushion film accordingto claim 1, wherein the self-adhesive compound is composed of butylrubber, the isoprene content of the butyl rubber being up to 1.8 molpercent.
 7. Self-adhesive air cushion film according to claim 1, whereinthe self-adhesive layer blended with elastomers, polyolefin copolymers,polybutenes, hydrogenated block copolymers of styrene and dienes oracrylate copolymers, the elastomers being present in an amount rangingfrom 0 to 20 parts by weight.
 8. Self-adhesive air cushion filmaccording to claim 1, wherein the self-adhesive compound is composed ofa polar component A and an apolar component B, the polar component Abeing present in an amount of 50% to 99% by weight and consisting of acopolymer or mixture of copolymers of ethylene and vinyl acetate whosevinyl acetate content is between 40% and 80% by weight, and the apolarcomponent B being present in an amount of 1% to 50% by weight andconsisting of one or a mixture of homopolymers or copolymers ofα-olefins having 2 to 12 carbon atoms, these polymers being saturated inthe main chain and being amorphous or having a low degree ofcrystallinity.
 9. Self-adhesive air cushion film according to claim 1,wherein the self-adhesive compound is composed of a polar component Aand an apolar component B, the polar component A being present in anamount of 50% to 99% by weight and consisting of a copolymer or mixtureof copolymers of ethylene and vinyl acetate whose vinyl acetate contentis between 40% and 80% by weight, and the apolar component B beingpresent in a fraction of 1% to 50% by weight and consisting ofcopolymers of α-olefins of 2 to 12 carbon atoms and nonconjugateddienes.
 10. Self-adhesive air cushion film according to claim 1, whereinthe self-adhesive compound is composed of polyethylene-vinyl acetatehaving a vinyl acetate content of 40% to 80% by weight, and a loss angletan δ of 0.6 to 1.0, measured at a temperature of 60° C. and a frequencyof 10⁻² Hz, and of 0.4 to 0.7, measured at a temperature of 60° C. and afrequency of 10 Hz.
 11. Self-adhesive air cushion film according toclaim 1, wherein the self-adhesive layer is blended with one or moreadditives selected from the group consisting of tackifiers,plasticizers, organic or inorganic fillers, pigments, light stabilizers,aging inhibitors, primary and secondary antioxidants, crosslinkingagents and crosslinking promoters.
 12. Process for producing theself-adhesive air cushion film of claim 1, which comprises receiving thesecond carrier film from an extruder and casting it through a die onto atransfer roll, which lays the second carrier film onto a thermoformingroll, containing bubble-shaped depressions and a vacuum zone, drawingthe second carrier film into the depressions in the thermoforming rollas it traverses the vacuum zone of the thermoforming roll therebyforming the bubbles, immediately following departure of the secondcarrier film from the vacuum section of the thermoforming roll, applyinga first carrier film from an extruder, through a die onto a furthertransfer roll and transferring said first carrier film from the furthertransfer roll to the thermoformed second carrier film, applying a sheetof polyethylene, provided with a self-adhesive layer, in a laminatingstation, consisting of rolls, to the bubbles in the second carrier film,with application of pressure, which flattens the air-filled bubbles atthe tip but does not compress them, and applying hot air atapproximately 180° C. through a hot-air nozzle into the nip formed bythe sheet of polyethylene and the second carrier film as the sheet ofpolyethylene is applied to the second carrier film, so that the sheet ofPolyethylene is inseparably welded to the tips of the bubbles.
 13. Amethod for protecting freshly painted surfaces of automobiles orautomobile parts as during assembly and/or transit which comprisesapplying the self-adhesive air cushion film of claim 1 to said surfaces.14. A method for protecting sensitive paint, metal, wood, plastic orglass surfaces which comprises applying the self-adhesive air cushionfilm of claim 1 to said surfaces.
 15. Self-adhesive air cushion filmaccording to claim 6, wherein the isoprene content of the butyl rubberis up to 1.2 mol percent.
 16. Self-adhesive air cushion film accordingto claim 7, wherein said elastomers are polyisobutylenes, saidpolyolefin copolymers are EPM or EPDM, and the elastomers are present inamounts of less than 10 parts by weight per 100 parts by weight of butylrubber.
 17. Self-adhesive air cushion film according to claim 10,wherein said vinyl acetate content is 70% by weight.